Waveguide structure and method for forming the same

ABSTRACT

An optical attenuating structure is provided. The optical attenuating structure includes a substrate, a waveguide, doping regions, an optical attenuating member, and a dielectric layer. The waveguide is extended over the substrate. The doping regions are disposed over the substrate, and include a first doping region, a second doping region opposite to the first doping region and separated from the first doping region by the waveguide, a first electrode extended over the substrate and in the first doping region, and a second electrode extended over the substrate and in the second doping region. The first optical attenuating member is coupled with the waveguide and disposed between the waveguide and the first electrode. The dielectric layer is disposed over the substrate and covers the waveguide, the doping regions and the first optical attenuating member.

BACKGROUND

An optical attenuator, or a fiber optic attenuator, is a device used toreduce the power level of an optical signal, either in free space or inan optical fiber. Optical attenuators are commonly used in fiber opticcommunications, either to test power level margins by temporarily addinga calibrated amount of signal loss, or installed permanently to properlymatch transmitter and receiver levels. Sharp bends stress optic fibersand can cause losses. If a received signal is too strong a temporary fixis to wrap the cable around a pencil until the desired level ofattenuation is achieved. However, such arrangements are unreliable,since the stressed fiber tends to break over time.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a schematic 3D diagram of an optical attenuating structure inaccordance with some embodiments of the present disclosure.

FIG. 2 is schematic side view of the optical attenuating structure ofFIG. 1.

FIG. 3 is a schematic 3D diagram of an optical attenuating structure inaccordance with some embodiments of the present disclosure.

FIG. 4 is schematic side view of the optical attenuating structure ofFIG. 3.

FIG. 5 is a schematic 3D diagram of an optical attenuating structure inaccordance with some embodiments of the present disclosure.

FIG. 6 is schematic side view of the optical attenuating structure ofFIG. 5.

FIG. 7 is a schematic 3D diagram of an optical attenuating structure inaccordance with some embodiments of the present disclosure.

FIG. 8 is schematic side view of the optical attenuating structure ofFIG. 7.

FIG. 9 is a schematic 3D diagram of an optical attenuating structure inaccordance with some embodiments of the present disclosure.

FIG. 10 is schematic side view of the optical attenuating structure ofFIG. 9.

FIG. 11 is a schematic 3D diagram of an optical attenuating structure inaccordance with some embodiments of the present disclosure.

FIG. 12 is schematic side view of the optical attenuating structure ofFIG. 11.

FIG. 13 is a schematic 3D diagram of an optical attenuating structure inaccordance with some embodiments of the present disclosure.

FIG. 14 is schematic side view of the optical attenuating structure ofFIG. 13.

FIG. 15 is a schematic 3D diagram of an optical attenuating structure inaccordance with some embodiments of the present disclosure.

FIG. 16 is schematic side view of the optical attenuating structure ofFIG. 15.

FIG. 17 is a flow chart of the method for forming an optical attenuatingstructure in accordance with different embodiments of the presentdisclosure.

FIGS. 18-27 are cross sections of an optical attenuating structure atdifferent stages of a method according to some embodiments of thepresent disclosure.

FIGS. 28-29 are cross sections of an optical attenuating structure atdifferent stages of a method according to some embodiments of thepresent disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of elements and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “over,” “upper,” “on” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

As used herein, although the terms such as “first,” “second” and “third”describe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another. The termssuch as “first,” “second” and “third” when used herein do not imply asequence or order unless clearly indicated by the context.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the disclosure are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in therespective testing measurements. Also, as used herein, the terms“substantially,” “approximately” and “about” generally mean within avalue or range that can be contemplated by people having ordinary skillin the art. Alternatively, the terms “substantially,” “approximately”and “about” mean within an acceptable standard error of the mean whenconsidered by one of ordinary skill in the art. People having ordinaryskill in the art can understand that the acceptable standard error mayvary according to different technologies. Other than in theoperating/working examples, or unless otherwise expressly specified, allof the numerical ranges, amounts, values and percentages such as thosefor quantities of materials, durations of times, temperatures, operatingconditions, ratios of amounts, and the likes thereof disclosed hereinshould be understood as modified in all instances by the terms“substantially,” “approximately” or “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thepresent disclosure and attached claims are approximations that can varyas desired. At the very least, each numerical parameter should at leastbe construed in light of the number of reported significant digits andby applying ordinary rounding techniques. Ranges can be expressed hereinas from one endpoint to another endpoint or between two endpoints. Allranges disclosed herein are inclusive of the endpoints, unless specifiedotherwise.

A variable optical attenuator (VOA) is widely used forwavelength-division-multiplexed (WDM) optical system for equalization ofsignals. A laser signal may pass through a splitter to generate aplurality of optical signals with different wavelength, and the VOA isto equalize the optical signals by providing large attenuation to makeallowable optical power level. The VOA is also proved at the receiversite before the signals are transmitted to an optical detector andconverting into electrical signals. A VOA includes a forwarded p-i-njunction structure, and a forwarded bias voltage is provided to createan optical loss for better equalization. Free carriers in a waveguide ofthe VOA result in current-controlled variable attenuation when applyingthe forwarded bias voltage, however, it results in high injectioncurrent and large power consumption in order to achieve a defaultoptical loss (e.g. greater than 30 dB of optical loss) to a certainwavelength (or a certain range of wavelength).

The present disclosure provides a VOA structure including an opticalattenuating member in order to achieve the default optical loss withlower power consumption. The optical signal is affected by thesurrounding environment, and thus the optical attenuating member isdesigned to be formed adjacent to the waveguide to provide optical lossof a target wavelength (or a target range of wavelengths). Some opticalloss of the default optical loss is attributed to the opticalattenuating member, and thus the same default optical loss required onthe target wavelength (or the target range of wavelengths) can beachieved by a lower power consumption. The present disclosure may alsoinclude a heater to adjust a phase of a wavelength in order to furthertuning the target wavelength and a performance of the VOA structure.

FIG. 1 shows an optical attenuating structure OA1 in accordance withsome embodiments of the present disclosure. The optical attenuatingstructure OA1 includes a substrate 11, a waveguide 12 and doping regions13. In some embodiments, the substrate 11 is a semiconductive substrate.In some embodiments, the substrate 11 includes an elementarysemiconductive substrate, such as silicon or germanium; a compoundsemiconductor substrate, such as silicon germanium, silicon carbide,gallium arsenic, gallium phosphide, indium phosphide, or indiumarsenide; or combinations thereof. In some embodiments, the waveguide 12includes same or similar material to a material of the substrate 11. Insome embodiments, a sum of a height H12 of the waveguide 12 and a heightH11 of the substrate 11 can be adjusted according to different bands ofdifferent applications, wherein the height H12 and the height H11 aremeasured along a Z direction. In some embodiments, the sum of the heightH12 and the height H11 is in a range of 100 nm-500 nm. In someembodiments, the sum of the height H12 and the height H11 is in a rangeof 200 nm-300 nm. In some embodiments, a width W12 of the waveguide 12is in a range of 250 nm-2 um, wherein the width W12 is measured along anX direction or an extending direction of the substrate 11. In someembodiments, the width W12 is in a range of 300 nm-500 nm. A length L12of the waveguide 12 measured along a Y direction or a longitudinaldirection of the waveguide 12 depends on a distance for propagation ofthe optical signal, and it is not limited herein.

The doping regions 13 are disposed over the substrate 11. The dopingregions 13 include a first doping region R131 and a second doping regionR132. The second doping region R132 is opposite to the first dopingregion R131 and separated from the first doping region R131 by thewaveguide 11. The first doping region R131 includes a first type ofdopants and the second doping region R132 includes a second type ofdopants different from the first type of dopants. In some embodiments,the first doping region R131 is a P-type doping region (or a positiveregion of the doping regions 13), and the second doping region R132 isan N-type doping region (or a negative region of the doping regions 13).In some embodiments, the first doping region R131 is an N-type dopingregion (or a negative region), and the second doping region R132 is aP-type doping region (or a positive region).

An intrinsic region R133 of the doping regions 13 is defined by thefirst doping region R131 and the second doping region R132. Theintrinsic region R133 is disposed between the first doping region R131and the second doping region R132 to form a core region. When a forwardbias voltage is applied to the doping regions 13, free carriers in thefirst doping regions R131 and the second doping region R132 are forcedand injected into the core region (i.e. the intrinsic region R133). Theinjected free carriers then absorb light in the waveguide 12, resultingin optical attenuation. The waveguide 12 is disposed in the intrinsicregion R133. A dimension D133 of the intrinsic region R133, which ismeasured as a distance D133 between the first doping region R131 and thesecond doping region R132 along an extending direction of the substrate11 (i.e. X direction in the embodiments of FIG. 1), depends on differentrequirements or devices, and it is not limited herein. In addition, adimension D131 of the first doping region R131 and a dimension D132 ofthe second doping region R132 can be adjusted depending on differentrequirements or devices, and they are not limited herein, wherein thedimension D131 and the dimension D132 are measured along the extendingdirection of the substrate 11 of the X direction.

The dimension D131 and the dimension D132 can be substantially the sameor different according to different applications. In some embodiments,the first doping region R131 includes different doping concentrations.In some embodiments, a first portion of the first doping region R131covering a first electrode 131 has a higher doping concentration thanthat of a second portion of the first doping region R131 proximal to theintrinsic region R133. In some embodiments, a first portion of thesecond doping region R132 covering a second electrode 131 has a higherdoping concentration than that of a second portion of the second dopingregion R132 proximal to the intrinsic region R133. In some embodiments,the first portion of the first doping region R131 and the first portionof the second doping region R132 respectively are greater than 1e20atoms/cm³. In some embodiments, the second portion of the first dopingregion R131 and the second portion of the second doping region R132respectively are in a range of 1e16-1e21 atoms/cm³ for a betterperformance of attenuation. In some embodiments, the second portion ofthe first doping region R131 and the second portion of the second dopingregion R132 respectively are in a range of 1e17-1e18 atoms/cm³ for agreater signal loss. A higher doping concentration can provide greatersignal loss but with greater power consumption and insertion loss as atradeoff. Therefore, the doping concentrations of the first and secondportions of the first doping region R131 and the first and secondportions of the second doping region R132 respectively can be adjustedaccording to different applications and requirements. In someembodiments, for a purpose of better performance of attenuation, a ratioof the doping concentrations between the first doping region R131 andthe second doping region R132 is in a range of 1 to 100, wherein theP-type doping concentration is equal to or higher than the N-type doingconcentration. In some embodiments, the ratio of P-type dopingconcentration to the N-type doping concentration is in a range of 1 to10 Different regions of the first doping region R131 and the seconddoping region R132 with different concentrations are not shown in FIG. 1but will be further illustrated in the following descriptionaccompanying with figures.

The first electrode 131 is disposed over the substrate 11 and in thefirst doping region R131. The second electrode is disposed over thesubstrate 11 and in the second doping region R132. The first electrode131 and the second electrode 132 are extended along the substrate 11. Insome embodiments, the first electrode 131, the second electrode 132 andthe waveguide 11 are extended along the same direction (e.g. Ydirection). In some embodiments, the first electrode 131, the secondelectrode 132 and the waveguide 11 are substantially parallel to eachother. In some embodiments, a height H131 of the first electrode 131 anda height H132 of the second electrode 132 respectively are substantiallyequal to the height H12 of the waveguide 12, wherein the height H131 andthe height H132 are measured along the Y direction. A length L131 of thefirst electrode 132 and a length L132 of the second electrode 132, whichare measured along the Y direction, are substantially equal to thelength L12 of the waveguide 12.

The optical attenuating structure OA1 further includes a first opticalattenuating member 14 and a second optical attenuating member 15. Thefirst optical attenuating member 14 and the second optical attenuatingmember 15 are coupled with the waveguide 12. The first opticalattenuating member 14 is disposed over the substrate 11 and between thewaveguide 12 and the first electrode 131. The second optical attenuatingmember 15 is disposed over the substrate 11 and between the waveguide 12and the second electrode 1323. In some embodiments, the first opticalattenuating member 14 is disposed in the first doping region R131. Insome embodiments, the second optical attenuating member 15 is disposedin the second doping region R132.

The first optical attenuating member 14 and the second opticalattenuating member 15 can affect optical signals transmitted in theoptical attenuating structure OA1. In some embodiments, the opticalattenuating structure OA1 can include only one of the first opticalattenuating member 14 and the second optical attenuating member 15. Insome embodiments, due to symmetrical pattern of a wavelength, the firstoptical attenuating member 14 and the second optical attenuating member15 are symmetrically disposed with respect to the waveguide 12.Configurations of the first optical attenuating member 14 and the secondoptical attenuating member 15 are not limited herein as long as astructural difference facing the waveguide 12 is present.

In the embodiment of FIG. 1, the first optical attenuating member 14includes a first portion 141 and a second portion 142. The first portion141 and the second portion 142 are arranged alternately along alongitudinal direction (e.g. the Y direction) of the first electrode 13.A height H141 of the first portion 141 is substantially equal to aheight H142 of the second portion 142, wherein the height H141 and theheight H142 are measured above the substrate and along the Z direction,or a direction substantially perpendicular to the extending direction ofthe substrate 11 and the longitudinal direction of the first electrode131. In the embodiment of FIG. 1, the height H141 and the height H142are substantially equal to the height H131, the height H132 and/or theheight H12.

In the embodiment of FIG. 1, a width W141 of the first portion 141 and awidth W142 of the second portion 142 are different, and thus the firstoptical attenuating member 14 can provide signal loss even the heightH131 and the height H132 are substantially the same. As shown in FIG. 1,the width W141 of the first portion 141 is less than the width W142 ofthe second portion 142 of the first optical attenuating member 14,wherein the width W141 and the width W142 are measured along the Xdirection. in other embodiments, the width W141 of the first portion 141can be greater than the width W142 of the second portion 142, and it isnot limited herein. A length L141 of the first portion and a length L142of the second portion can be substantially equal or different, whereinthe length L141 and the length L142 are measured along the Y directionor the longitudinal direction of the first electrode 131. In theembodiments of FIG. 1, the length L141 is greater than the length L142for a purpose of illustration but not a limitation.

The first optical attenuating member 14 can include one or moreportions. FIG. 1 shows two portions 141 and 142 are for illustrationonly. Lengths, widths, and heights of different portions of the firstoptical attenuating member 14 are adjusted according to different targetwavelengths for attenuation. In some embodiments, the first opticalattenuating member 14 includes more than two different portionsalternately arranged along the Y direction. In some embodiments, thefirst optical attenuating member 14 includes only the first portion 141or the second portion 142.

A length L14 of the first optical attenuating member 14 can be adjusteddepending on a target signal loss by the first optical attenuatingmember 14. The length L14 is measured along the Y direction between twoedges of the first optical attenuating member 14, the length L14 canalso be understood as a total length of the first optical attenuatingmember 14. In the embodiments of FIG. 1, the length L14 is substantiallyequal to the length L131 of the first electrode 13 of the length L12 ofthe waveguide 12. In other embodiments, the length L14 is less than thelength L131 of the first electrode 13 of the length L12 of the waveguide12. A greater length L14 of the first optical attenuating member 14provide a greater signal loss.

In some embodiments, the second optical attenuating member 15 and thefirst optical attenuating member 14 are symmetrical with respect to thewaveguide 12. In the embodiments of FIG. 1, a first portion 151 of thesecond optical attenuating member 15 is substantially identical to thefirst portion 141 of the first optical attenuating member 14, and asecond portion 152 of the second optical attenuating member 15 issubstantially identical to the second portion 142 of the first opticalattenuating member 14. Thus, a detailed configuration of the secondoptical attenuating member 15 is not repeated herein. In addition, itshould be noted that the substrate 11, the waveguide 12, the firstelectrode 131, the second electrode 132, the first portion 141 and thesecond portion 142 of the first optical attenuating member 141, and thefirst portion 151 and the second portion 152 of the second opticalattenuating member 142 are illustrated as individual features in FIG. 1,but it is for a purpose of illustration. In some embodiments, two ormore of the waveguide 12, the first electrode 131, the second electrode132, the first portion 141 and the second portion 142 of the firstoptical attenuating member 141, and the first portion 151 and the secondportion 152 of the second optical attenuating member 142 can bemonolithic.

The optical attenuating structure OA1 further includes a dielectriclayer 16 disposed over the substrate 11 and covering the waveguide 12,the doping regions13, the first optical attenuating member 14 and thesecond optical attenuating member 15. The dielectric layer 16 may befurther disposed under the substrate 11 to surround the entire substrate11. In some embodiments, the dielectric layer includes one or more ofsilicon oxide (SiOx), germanium oxide (GeOx), silicon nitride (SiNx) andsilicon oxynitride (SiON). In some embodiments, the dielectric layer 16is disposed under an interconnect structure (not shown) for electricalpath between the optical attenuating structure OA1 and exteriorelectrical devices. The interconnect structure can includes a pluralityof inter-metal dielectric (IMD) layers and a plurality of layers ofmetal lines. In some embodiments, the dielectric layer 12 forms aportion of the plurality of inter-metal dielectric (IMD) layers of theinterconnect structure.

FIG. 2 is a side view of the optical attenuating structure OA1 ofFIG. 1. A distance D12 a between the waveguide 12 and the firstelectrode 131 is in a range of 500 nm-2 um, wherein the distance D12 ais measured along the X direction. A trade-off between propagation lossand a bandwidth is adjusted to have a suitable value of the distance D12a. In some embodiments, a distance D12 b between the waveguide 12 andthe second electrode 15 is substantially equal to the distance D12 a dueto symmetrical arrangement of the first optical attenuating member 14and the second optical attenuating member 15 with respect to thewaveguide 12. A width W14 of the first optical attenuating member 14 isin a range of 5 nm-50 nm or 1/20˜/200 of distance D12 a, wherein thewidth W14 is measured along the X direction and can be understood as atotal width (or a greatest width) of the first optical attenuatingmember 14.

In order to further illustrate concepts of the present disclosure,various embodiments are provided below. However, it is not intended tolimit the present disclosure to specific embodiments. In addition,elements, conditions or parameters illustrated in different embodimentscan be combined or modified to have different combinations ofembodiments as long as the elements, parameters or conditions used arenot conflicted. For ease of illustration, reference numerals withsimilar or same functions and properties are repeatedly used indifferent embodiments and figures, but it does not intend to limit thepresent disclosure into specific embodiments. For a purpose of brevity,only differences from other embodiments are emphasized in the followingspecification, and descriptions of similar or same elements, functionsand properties are omitted.

FIG. 3 shows an optical attenuating structure OA2 in accordance withsome embodiments of the present disclosure. FIG. 4 is a side view of theoptical attenuating structure OA2 as shown in FIG. 3. The opticalattenuating structure OA2 includes different portions of the firstoptical attenuating member 14 having different heights. In theembodiments as shown in FIGS. 3-4, the second optical attenuating member15 also includes different portions with different heights. In theembodiments, the width W14 of the first optical attenuating member 14 isconsistent along its length (e.g. the Y direction). In the embodiments,the width W141 of the first portion 141 and the width W142 of the secondportion 142 of the first optical attenuating member 14 are substantiallyequal, and the height H141 of the first portion 141 is less than theheight H142 of the second portion 142. In the embodiments shown in FIGS.3-4, the height H142 of the second portion 142 is also less than theheight H131 of the first electrode 131 or the height H12 of thewaveguide 12. However, in other embodiments, the height H142 of thesecond portion 142 can be substantially equal to the height H131 of thefirst electrode 131 or the height H12 of the waveguide 12.

FIG. 5 shows an optical attenuating structure OA3 in accordance withsome embodiments of the present disclosure. FIG. 6 is a side view of theoptical attenuating structure OA3 as shown in FIG. 5. The opticalattenuating structure OA3 includes different portions of the firstoptical attenuating member 14 having different heights and differentwidths. In the embodiments as shown in FIGS. 5-6, the second opticalattenuating member 15 also includes different portions with differentheights and different widths. The width W141 of the first portion 141 isless than the width W142 of the second portion 142 of the first opticalattenuating member 14, and the height H141 of the first portion 141 isalso less than the height H142 of the second portion 142. In theembodiments shown in FIGS. 3-4, the height H141 of the first portion 141and the height H142 of the second portion 142 are both less than theheight H131 of the first electrode 131 or the height H12 of thewaveguide 12. In other words, a height H14 of the first opticalattenuating member 14 is less than the height H12 of the waveguide,wherein the height H14 is measured along the Y direction and can beunderstood as a total height (or a greatest height) of the first opticalattenuating member 14. However, in other embodiments, the height H142 ofthe second portion 142 can be substantially equal to the height H131 ofthe first electrode 131 or the height H12 of the waveguide 12. In theembodiments, the width W14 of the first optical attenuating member 14 issubstantially equal to width W142 of the second portion 142.

FIG. 7 shows an optical attenuating structure OA4 in accordance withsome embodiments of the present disclosure. FIG. 8 is a side view of theoptical attenuating structure OA4 as shown in FIG. 7. The opticalattenuating structure OA4 also includes different portions of the firstoptical attenuating member 14 having different heights along its width(e.g. the X direction). The first portion 141 is disposed proximal tothe waveguide 12, and the second portion 142 is disposed proximal to thefirst electrode 131. In the embodiments, the first portion 141 is incontact with the second portion 142. The height H141 of the firstportion 141 and the height H142 of the second portion 142 are both lessthan the height H131 of the first electrode 131 or the height H12 of thewaveguide 12, and the height H141 of the first portion 141 is less thanthe height H142 of the second portion 142. Thus, the first portion 141and the second portion 142 together to define a stair configuration ofthe first optical attenuating member 14 having a height graduallydecreased from the first electrode 14 toward the waveguide 12 along theX direction. Specific heights of each of first portion 141 and thesecond portion 142 are not limited herein. In the embodiments, theheight H141 is about ⅓ of the height H131 of the first electrode 131,and the height H142 of the second portion 142 is about ⅔ of the heightH131 of the first electrode 131. Due to the arrangement of the firstportion 141 and the second portion 142, the width W14 of the firstelectrode 14 is equal to a sum of the width W141 and the width W142 inthe embodiments. Each of the width W141 of the first portion 141 and thewidth W142 of the second portion 142 of the first optical attenuatingmember 14 is not limited herein. In the embodiments, the first widthW141 and the width W142 are substantially equal to each other.

FIG. 9 shows an optical attenuating structure OA5 in accordance withsome embodiments of the present disclosure. FIG. 10 is a side view ofthe optical attenuating structure OA5 as shown in FIG. 9. In theembodiments, the optical attenuating structure OA5 includes a pluralityof portions 14 a, 14 b and 14 c of the first optical attenuating member14. The plurality of portions 14 a, 14 b and 14 c are separatelyarranged along the Y direction or the longitudinal direction of thewaveguide 12. In the embodiments, the portions 14 a, 14 b and 14 c aresubstantially identical, but the present disclosure is not limitedherein. In the embodiments, the first optical attenuating member 14 isseparated from the waveguide 12 and the first electrode 14. A distanceD14 a between the first optical attenuating member 14 and the firstelectrode 131 and a distance D14 b between the first optical attenuatingmember 14 and the waveguide 12 can be designed and adjusted according todifferent applications, and they are not limited herein. Similar to theillustration in other embodiments, the height H14, the width W14, alength of one portion of the first optical attenuating member 14, andthe total length L14 of the first optical attenuating member 14 can beadjusted according to different target wavelengths and different targetsignal losses.

Therefore, the present disclosure provides an optical attenuatingstructure including an optical attenuating member in order to achieve adesired optical loss with lower power consumption. In order to ensurethe optical loss being of a target wavelength, an optical attenuatingstructure of the present disclosure can include a heater to shift aphase of a wavelength for tuning the target wavelength. For a purpose ofheat insulation, an optical attenuating structure of the presentdisclosure can also include one or more cavities adjacent to thewaveguide of the optical attenuating structure.

FIG. 11 shows an optical attenuating structure OA6 in accordance withsome embodiments of the present disclosure. FIG. 12 is a side view ofthe optical attenuating structure OA6 as shown in FIG. 11. The opticalattenuating structure OA6 is similar to the optical attenuatingstructure OA3 but further includes a heater 17 disposed over thewaveguide 12. FIGS. 11-12 are for a purpose of illustration, and theheater 17 can be disposed in other optical attenuating structuressimilar to any of the optical attenuating structures OA1-OA5. The heater17 is disposed in the dielectric layer 16 and separated from thewaveguide 12 and the doping regions 13. In some embodiments, the heater17 includes one or more metallic materials, such as titanium nitride(TiN), tantalum nitride (TaN), copper (Cu), aluminum (Al) and/or othersuitable pure metal or metal-containing materials. The heater 17 atleast vertically covers a portion of the waveguide 12 for a betterheating efficiency. In some embodiments, the heater 17 vertically coversthe entire waveguide 12. In some embodiments, a width W17 of the heater17 is at least greater than the width W12 of the waveguide 12, whereinthe width W17 is measured along the X direction. In some embodiments,the width W17 of the heater 17 is about two to five times of the widthW12 of the waveguide 12. In the embodiments shown in FIGS. 11-12, thewidth W17 of the heater 17 is substantially the same as a width W11 ofthe substrate 11, wherein the width W11 is measured along the Xdirection or an extending direction of the substrate 11. in someembodiments, the heater 17 covers the entire doping regions 13 or theentire substrate 11. A distance D17 between the heater 17 and thewaveguide 12 measured along the Z direction is in a range of 300 nm-500nm. In some embodiments, the heater 17 can be formed in one or more ofthe IMD layers, and a thickness of the heater 17 measured along the Zdirection depends on the thickness of the corresponding IMD layers.

As the semiconductor material of the waveguide 12 can be sensitive tothe temperature, the distance D17 is controlled being equal to orgreater than 300 nm to avoid unwanted signal loss due to a temperaturechange by the heater 17. For a purpose of heating efficiency, thedistance D17 is controlled being equal to or less than 500 nm to avoidunwanted heat loss and extra power consumption for operating the heater17.

FIG. 13 shows an optical attenuating structure OA7 in accordance withsome embodiments of the present disclosure. FIG. 14 is a side view ofthe optical attenuating structure OA7 as shown in FIG. 13. The opticalattenuating structure OA7 is similar to the optical attenuatingstructure OA6 but further includes a first cavity 18 disposed over theheater 17 for heat isolation. The cavity is formed in the dielectriclayer 16 and separated from the heater 17. The first cavity 18 at leastvertically covers a portion of the heater 17 for a better heatingisolation. In some embodiments, the first cavity 18 vertically coversthe entire heater 17. In some embodiments, a width W18 of the firstcavity 18 is at least greater than the width W12 of the waveguide 12,wherein the width W18 is measured along the X direction. In someembodiments, the width W18 of the heater 18 is about two to five timesof the width W12 of the waveguide 12. In some embodiments, the width W18of the first cavity 18 is at least substantially equal to or greaterthan the width W17 of the heater 17. In the embodiments shown in FIGS.11-12, the width W18 of the first cavity 18 is substantially the same asa width W17 of the heater 17. A distance D18 between the first cavity 18and the heater 17 measured along the Z direction is greater than zero.In some embodiments, the first cavity 18 and the heater 17 is separatedby the dielectric layer 16 for preventing oxidation or damage to theheater 17 from the air or environment. In some embodiments, the firstcavity 18 is filled with an air or a suitable gas.

FIG. 15 shows an optical attenuating structure OA8 in accordance withsome embodiments of the present disclosure. FIG. 16 is a side view ofthe optical attenuating structure OA8 as shown in FIG. 15. The opticalattenuating structure OA8 is similar to the optical attenuatingstructure OA7 but further includes a second cavity 19 disposed under thesubstrate 18 for heat isolation. The second cavity 19 is disposed in thedielectric layer 16 and separated from the substrate 11. The substrate11 is encapsulated by the dielectric layer 16 for protection of thesubstrate 11. Parameters of the second cavity 19 can be similar to thefirst cavity 18 as illustrated in FIGS. 13-14, and repeated descriptionis omitted herein. In the embodiments, the optical attenuating structureOA8 includes both the upper first cavity 18 and the lower second cavity19 for better heat isolation. In some embodiments, only the lower secondcavity 19 is included and enough for the required heat isolation.

In order to further illustrate the present disclosure, a method M10 forforming an optical attenuating structure is provided. FIG. 17 is a flowchart of the method M10. The method M10 includes several operations:(O101) receiving a substrate; (O102) removing portions of the substrateto form a plurality of protrusions with different heights; (O103)implanting the substrate with different types of dopants to form a firstdoping region and a second doping region separated from the first dopingregion; and (O104) forming a dielectric layer surrounding the substrate.In some embodiments, the method M10 further includes: (O105) forming ametal-containing layer in the dielectric layer over the substrate; and(O106) removing a portion of the dielectric over the metal-containinglayer.

FIGS. 18-27 are cross sections illustrating different stages ofmanufacturing an optical attenuating structure by the method M10according to some embodiments of the present disclosure.

In accordance with the operations O101 and O102 as shown in FIGS. 18-19,a substrate 11 is received. In some embodiments, the substrate 11includes semiconductive material. In some embodiments, the substrate 11is a silicon substrate. In some embodiments, the substrate 11 can be asilicon layer of a silicon-on-insulator (SOI) substrate. An etchingoperation is performed to remove portions of the substrate 11 to form aplurality of protrusions. As shown in FIG. 20, a first protrusion, asecond protrusion, a third protrusion are substantially parallel andrespectively define the first electrode 131, the second electrode 132and the waveguide 12. Fourth protrusions define the first opticalattenuating member 14 and the second optical attenuating member 15respectively. In the embodiment of FIG. 20, the fourth protrusionsinclude a greatest height less than a height of the first protrusion ora height of the second protrusion, similar to the embodiments shown inFIGS. 7-8. In the embodiments, the first optical attenuating member 14is connected to the first electrode 131, and the second opticalattenuating member 15 is connected to the second electrode 132. However,the present disclosure is not limited herein. As illustrated above indifferent embodiments, the first optical attenuating member 14 and thesecond optical attenuating member 15 can be separated from the firstelectrode 131 and the second electrode 132, and/or have differentconfigurations from a cross-sectional view.

The waveguide 12, the first electrode 131, the second electrode 132, thefirst optical attenuating member 14 and the second optical attenuatingmember 15 can be formed simultaneously or separately. In someembodiments, the waveguide 12, the first electrode 131, the secondelectrode 132, the first optical attenuating member 14 and the secondoptical attenuating member 15 can be formed by one or several times ofetching operations. In some embodiments, the etching operation includesa dry etching operation. In the operation O102, different amountsemiconductive material from a top surface S11 of the substrate 11 alonga depth direction (i.e. the Z direction in the embodiments) are removed.In some embodiments, a first portion of the substrate 11 in a firstamount and a second portion of the substrate 11 in a second amount areremoved. The first optical attenuating member 14 and the second opticalattenuating member 15 having different heights from those of thewaveguide 12, the first electrode 131 and the second electrode 132 canthereby formed. In some embodiments, a thickens T12 of the waveguide 12,a thickness T131 of the first electrode 131 and a thickness T132 of thesecond electrode 132 are substantially equal to a thickness of thesubstrate 11. The thickness T12, the thickness T131 and the thicknessT132 are measured from tops of the waveguide 12, the first electrode 131and the second electrode 132 respectively to a bottom of the substrate11 along the Z direction.

In accordance with the operation O103 as shown in FIG. 20, one or moretimes of implantations are performed on the substrate 11 to form thefirst doping region R131 having a first type of dopants and the seconddoping region R132 having second type of dopants different from thefirst type of dopants. Therefore, the protrusion defining the firstelectrode 131 has the first conductive type; the protrusion defining thesecond electrode 132 has the second conductive type different from thefirst conductive type; and the protrusion defining the waveguide 12 isin the intrinsic region R133. The first doping region R131 includes afirst higher doping region R131 a and a first lower doping region R131b. The first higher doping region R131 a has a higher dopingconcentration than that of the first lower doping region R131 b. Thefirst higher doping region R131 a covers at least the first electrode131. In some embodiments, the first higher doping region R131 a covers aportion of the first optical attenuating member 14. The first lowerdoping region R131 b covers a portion of the substrate 11 between thefirst electrode 131 and the waveguide 12. The first lower doping regionR131 b may cover at least a portion of the first optical attenuatingmember 14. In some embodiments, the first optical attenuating member 14is entirely disposed in the first lower doping region R131 b.

The second doping region R132 includes a second higher doping regionR132 a and a second lower doping region R132 b. The second higher dopingregion R132 a has a higher doping concentration than that of the secondlower doping region R132 b. The first higher doping region R131 a coversat least the second electrode 132. In some embodiments, the secondhigher doping region R132 a covers a portion of the second opticalattenuating member 15. The second lower doping region R132 b covers aportion of the substrate 11 between the second electrode 132 and thewaveguide 12. The second lower doping region R132 b may cover at least aportion of the second optical attenuating member 15. In someembodiments, the second optical attenuating member 15 is entirelydisposed in the second lower doping region R132 b. The second dopingregion R132 has a different type of dopant from that of the first dopingregion R131. As illustrated above, covering areas and dopingconcentrations of the first doping region R131 and the second dopingregion R132 depend on different applications. In some embodiments, oneor more masks are used to form the first doping region R131 and thesecond doping region R132.

In accordance with the operation O104 as shown in FIGS. 21-22, thedielectric layer 16 is formed to surround the substrate 11. Thedielectric layer 16 may be a multi-layer structure including aninsulating layer 165 of the SOI substrate and a first sub-layer 161formed over the SOI substrate encapsulating the substrate 11 as shown inFIG. 21. In some embodiments, the insulating layer 165 is a siliconoxide layer. In some embodiments, the dielectric layer 16 is amulti-layer structure and includes a plurality of sub-layers formed overthe insulating layer 165 as shown in FIG. 22. The dielectric layer 16may include the first sub-layer 161 surrounding the substrate 11 and asecond sub-layer 162 disposed over the first sub-layer 161. It should benoted that only one second sub-layer 162 over the first sub-layer 161 isdepicted for a purpose of illustration. In some embodiments, thedielectric layer 16 includes a plurality of sub-layers disposed over thesub-layer 161 and the insulating layer 165 of the SOI substrate.

In accordance with the operation O105 as shown in FIGS. 23-24, ametal-containing layer is disposed in the dielectric layer 16 over thesubstrate 11 to form the heater 17. A portion of the dielectric layer 16(or the sub-layer 162) is removed to form a cavity C17 to define aposition of the heater 17 as shown in FIG. 23. In some embodiments, thecavity C17 penetrates the sub-layer 162 and exposes a portion of thesub-layer 16. In some embodiments, the cavity C17 stops in the sub-layer162 without penetrating the sub-layer 162. Therefore, in someembodiments, a thickness of the heater 17 is equal to or less than athickness of the sub-layer 162. The metal-containing layer is formed inthe cavity C17. In some embodiments, the metal-containing layer isformed by a deposition operation. In some embodiments, a planarizationis performed after the metal-containing layer is formed in the cavityC17 to form the heater 17.

In some embodiments, one or more sub-layers of the dielectric layer 16are formed over the heater 17 as shown in FIG. 25. The heater 17 isembedded in the dielectric layer 16. The dielectric layer 16 including asub-layer 163 and a sub-layer 164 disposed over the heater 17 for apurpose of illustration. In some embodiments, a number of sub-layers ofthe dielectric layer 16 depends on a number of IMD layers of theinterconnect structure. In some embodiments, the sub-layer 164 is a topsub-layer of the dielectric layer 16 (or a top IMD layer of theinterconnect structure).

In accordance with the operation O106 as shown in FIG, 26, a portion ofthe dielectric layer 16 over the heater 17 is removed to form the upperfirst cavity 18. In some embodiments, the upper first cavity 18penetrates one or more sub-layers (e.g. the sub-layer 164 in FIG. 26) ofthe dielectric layer 16. In some embodiments, the upper first cavity 18stops at one of the sub-layer (e.g. the sub-layer 163 in FIG. 26) overthe heater 17.

In some embodiments, the lower second cavity 19 is optionally formed asshown in FIG. 27. A portion of the dielectric layer 16 under thesubstrate 11 (e.g. a portion of the insulating layer 165 of the SOIsubstrate) is removed to form the lower second cavity 19. In someembodiments, the structure shown in FIG. 26 is flipped over, and anetching operation is performed to form the lower second cavity 19. Itshould be noted that portions of the SOI substrate covering the lowersecond cavity 19 may also be removed in order to form the lower secondcavity 19.

In some embodiments, the upper first cavity 18 and/or the lower secondcavity 19 are opening cavities. In some embodiments, the upper firstcavity 18 and/or the lower second cavity 19 are closed cavities sealedby the dielectric layer.

In accordance with some embodiments as shown in FIGS. 28-29, the upperfirst cavity 18 is formed after formation of the sub-layer 163 and priorto formation of the sub-layer 164. Therefore, less thickness of thedielectric layer 16 is removed to form the upper first cavity 18, andthe upper first cavity 18 is sealed by the dielectric layer 16. In someembodiments, the upper first cavity 18 can penetrate multiple sub-layersof the dielectric layer 16. Similarly, the lower second cavity 19 canalso be sealed by another sub-layer of the dielectric layer 16 formedunder the substrate 11 and the lower second cavity 19 after formation ofthe lower second cavity 19 (not shown).

Some embodiments of the present disclosure provide an opticalattenuating structure. The optical attenuating structure includes asubstrate, a waveguide, doping regions, an optical attenuating member,and a dielectric layer. The waveguide is extended over the substrate.The doping regions is disposed over the substrate, and includes a firstdoping region, a second doping region opposite to the first dopingregion and separated from the first doping region by the waveguide, afirst electrode extended over the substrate and in the first dopingregion, and a second electrode extended over the substrate and in thesecond doping region. The first optical attenuating member is coupledwith the waveguide and disposed between the waveguide and the firstelectrode. The dielectric layer is disposed over the substrate andcovers the waveguide, the doping regions and the first opticalattenuating member.

Some embodiments of the present disclosure provide an opticalattenuating structure. The optical attenuating structure includes asilicon portion and a dielectric portion surrounding the siliconportion. The silicon portion includes a first protrusion, a secondprotrusion, a third protrusion and a fourth protrusion. The firstprotrusion has a first conductive type, and the second protrusion has asecond conductive type, different from the first conductive type. Thethird protrusion is disposed between the first protrusion and the secondprotrusion, wherein the first protrusion, the second protrusion, and thethird protrusion are substantially parallel. The fourth protrusion isdisposed between the first protrusion and the third protrusion wherein aheight of the fourth protrusion is less than a height of the firstprotrusion or a height of the second protrusion.

Some embodiments of the present disclosure provide a method for formingan optical attenuating structure. The method includes multipleoperations: receiving a semiconductor substrate; removing portions ofthe semiconductive substrate to form a plurality of protrusions withdifferent heights; implanting the semiconductor substrate with differenttypes of dopants to form a first doping region and a second dopingregion separated from the first doping region; and forming a dielectriclayer surrounding the semiconductor substrate.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. An optical attenuating structure, comprising: a substrate; awaveguide, extending along the substrate; a first doping region disposedover the substrate and extending along the waveguide; a second dopingregion opposite to the first doping region and separated from the firstdoping region by the waveguide; a first electrode extending along thesubstrate and in the first doping region; a second electrode extendingalong the substrate and in the second doping region; a first opticalattenuating member, coupled with the waveguide and disposed between thewaveguide and the first electrode; and a dielectric layer, disposed overthe substrate and covering the waveguide, the first and second dopingregions and the first optical attenuating member.
 2. The opticalattenuating structure of claim 1, wherein a height of the first opticalattenuating member is substantially less than a height of the firstelectrode or the second electrode.
 3. The optical attenuating structureof claim 1, wherein the waveguide, the first electrode and the secondelectrode are in parallel to each other.
 4. The optical attenuatingstructure of claim 1, wherein the substrate, the waveguide and the firstoptical attenuating member are monolithic.
 5. The optical attenuatingstructure of claim 1, further comprising: a heater, disposed in thedielectric layer over the waveguide.
 6. The optical attenuatingstructure of claim 1, further comprising: a cavity disposed over theheater or under the substrate.
 7. The optical attenuating structure ofclaim 1, wherein the first doping region includes a first type ofdopants, and the second doping region includes a second type of dopantsdifferent from the first type of dopants.
 8. The optical attenuatingstructure of claim 1, wherein the first optical attenuating member havedifferent widths along a longitudinal direction of the waveguide.
 9. Theoptical attenuating structure of claim 1, further comprising: a secondoptical attenuating member coupled with the waveguide and disposedbetween the waveguide and the second electrode, wherein the secondoptical attenuating member is substantially symmetrical to the firstoptical attenuating member with respect to the waveguide.
 10. An opticalattenuating structure, comprising: a silicon portion, comprising: afirst protrusion, having a first conductive type; a second protrusion,having a second conductive type, different from the first conductivetype; a third protrusion, disposed between the first protrusion and thesecond protrusion, wherein the first protrusion, the second protrusion,and the third protrusion are substantially parallel; and a fourthprotrusion, disposed between the first protrusion and the thirdprotrusion, wherein a height of the fourth protrusion is less than aheight of the first protrusion or a height of the second protrusion; anda dielectric portion, surrounding the silicon portion.
 11. The opticalattenuating structure of claim 10, wherein the fourth protrusion has astair configuration.
 12. The optical attenuating structure of claim 10,wherein the fourth protrusion comprises a first portion and a secondportion alternately arranged along a longitudinal direction of the thirdprotrusion, and the second portion has a dimension greater than adimension of the first portion.
 13. The optical attenuating structure ofclaim 10, wherein the fourth protrusion comprises a plurality ofportions separately arranged along a longitudinal direction of the thirdprotrusion.
 14. The optical attenuating structure of claim 10, whereinthe fourth protrusion is separated from the first protrusion and thesecond protrusion.
 15. The optical attenuating structure of claim 10,wherein the fourth protrusion is connected to the first protrusion. 16.The optical attenuating structure of claim 10, wherein the fourthprotrusion includes a first portion having a first doping concentrationand a second portion having a second doping concentration different fromthe first doping concentration.
 17. The optical attenuating structure ofclaim 15, wherein a first portion of the fourth protrusion proximal tothe first protrusion has a doping concentration greater than a dopingconcentration of a second portion of the fourth protrusion proximal tothe third protrusion, and the first portion is adjacent to the secondportion.
 18. A method of manufacturing an optical attenuating structure,comprising: receiving a substrate; removing portions of the substrate toform a plurality of protrusions with different heights; implanting thesemiconductor substrate with different types of dopants to form a firstdoping region and a second doping region separated from the first dopingregion; and forming a dielectric layer to surround the substrate. 19.The method of claim 18, wherein the plurality of protrusions withdifferent heights are formed simultaneously.
 20. The method of claim 18,wherein the removal of the portions of the substrate including removinga first portion of the substrate in a first amount and removing a secondportion of the substrate in a second amount different from the firstamount.